The Khmer Rouge had been considered all but crushed after its last stronghold fell to government troops in April and longtime leader Pol Pot died the same month.

Despite Friday's attack, however, the group is unlikely to have much impact on the July 26 election.

About five guerrillas opened fire on the election officials as their convoy traveled between Anlong Veng, the captured Khmer Rouge base in northern Cambodia, and Trapeang Prasat, about 10 miles east, regional military chief Maj. Gen. Chea Mann said.

They were carrying election materials to former Khmer Rouge fighters who have defected to the government and are receiving instructions on how to participate in the election.

The dead men were identified as security officers.

An election commission official also was wounded.

"It is Khmer Rouge under the command of Ta Mok from along the border," Chea Mann said. "They are trying to disrupt the elections."

Gen. Ta Mok, known as "The Butcher" for his revolutionary brutality, seized control from Pol Pot last year.

He is believed to control only a few hundred guerrillas along the rugged border with Thailand.

The Khmer Rouge has nearly disappeared because of mass defections during the past two years. In 1993, they still numbered more than 10,000 fighters but were unable to wreak the havoc they had promised on U.N.-organized elections then.

The Maoist-inspired movement caused the deaths of as many as 2 million Cambodians between 1975 and 1979. They were toppled by an invasion by Vietnam, Cambodia's historic enemy. A decade of harsh military occupation followed.

Hun Sen, who came to power under the Vietnamese, has been widely accused of using violence and intimidation to ensure his victory.

On Saturday, prominent opposition leader Sam Rainsy warned that Hun Sen was deploying troops to frighten people into voting for him. Sam Rainsy maintains that Hun Sen will either try to disqualify the opposition or simply call out the army to retain power if he loses.

Hun Sen, meanwhile, was recovering from an emergency appendectomy and was expected to stay bedridden for the campaign's final week.

Hun Sen deposed the other main opposition candidate, Prince Norodom Ranariddh, as co-prime minister in a bloody coup last year. Ranariddh's royalist party had won the 1993 elections, but Hun Sen threatened civil war if not given a joint premiership. Diplomatic pressure and the desire for international legitimacy and aid led Hun Sen to call new elections.